add remote.<name>.annex-checkuuid

Added remote.<name>.annex-checkuuid config, which can be set to false to
disable the default checking of the uuid of remotes that point to
directories. This can be useful to avoid unncessary drive spin-ups and
automounting.

Note that the UUID check is still done before writing to the repository,
to avoid writing to the wrong repository if it got relocated. Check is
also done before checkPresent to avoid getting confused about what is in
which repo. This is effectively the same as the use of git-annex-shell
with a uuid to check that the remote repository is the expected one.
Did not bother with the check for retrieveKeyFile because it doesn't
matter if the wrong repo is used then.

This commit was sponsored by Trenton Cronholm on Patreon.

6 files changed, 97 insertions, 26 deletions

diff --git a/CHANGELOG b/CHANGELOG
index fe5dba4cd..32fbcabad 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -16,6 +16,10 @@ git-annex (6.20171215) UNRELEASED; urgency=medium
   * Improve startup time for commands that do not operate on remotes,
     and for tab completion, by not unnessessarily statting paths to
     remotes, which used to cause eg, spin-up of removable drives.
+  * Added remote.<name>.annex-checkuuid config, which can be set to false
+    to disable the default checking of the uuid of remotes that point to
+    directories. This can be useful to avoid unncessary drive spin-ups and
+    automounting.
 
  -- Joey Hess <id@joeyh.name>  Wed, 20 Dec 2017 12:11:46 -0400
 
diff --git a/Remote/Git.hs b/Remote/Git.hs
index 8df14937e..2cebcce4a 100644
--- a/Remote/Git.hs
+++ b/Remote/Git.hs
@@ -1,6 +1,6 @@
 {- Standard git remotes.
  -
- - Copyright 2011-2017 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2018 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -123,7 +123,8 @@ gitSetup (Enable _) (Just u) _ c _ = do
 gitSetup (Enable _) Nothing _ _ _ = error "unable to enable git remote with no specified uuid"
 
 {- It's assumed to be cheap to read the config of non-URL remotes, so this is
- - done each time git-annex is run in a way that uses remotes.
+ - done each time git-annex is run in a way that uses remotes, unless
+ - annex-checkuuid is false.
  -
  - Conversely, the config of an URL remote is only read when there is no
  - cached UUID value. -}
@@ -134,7 +135,9 @@ configRead autoinit r = do
 	annexignore <- liftIO $ getDynamicConfig (remoteAnnexIgnore gc)
 	case (repoCheap r, annexignore, u) of
 		(_, True, _) -> return r
-		(True, _, _) -> tryGitConfigRead autoinit r
+		(True, _, _)
+			| remoteAnnexCheckUUID gc -> tryGitConfigRead autoinit r
+			| otherwise -> return r
 		(False, _, NoUUID) -> tryGitConfigRead autoinit r
 		_ -> return r
 
@@ -142,22 +145,24 @@ gen :: Git.Repo -> UUID -> RemoteConfig -> RemoteGitConfig -> Annex (Maybe Remot
 gen r u c gc
 	| Git.GCrypt.isEncrypted r = Remote.GCrypt.chainGen r u c gc
 	| otherwise = case repoP2PAddress r of
-		Nothing -> go <$> remoteCost gc defcst
+		Nothing -> do
+			duc <- mkDeferredUUIDCheck r u gc
+			go duc <$> remoteCost gc defcst
 		Just addr -> Remote.P2P.chainGen addr r u c gc
   where
 	defcst = if repoCheap r then cheapRemoteCost else expensiveRemoteCost
-	go cst = Just new
+	go duc cst = Just new
 	  where
 		new = Remote 
 			{ uuid = u
 			, cost = cst
 			, name = Git.repoDescribe r
-			, storeKey = copyToRemote new
+			, storeKey = copyToRemote new duc
 			, retrieveKeyFile = copyFromRemote new
 			, retrieveKeyFileCheap = copyFromRemoteCheap new
-			, removeKey = dropKey new
-			, lockContent = Just (lockKey new)
-			, checkPresent = inAnnex new
+			, removeKey = dropKey new duc
+			, lockContent = Just (lockKey new duc)
+			, checkPresent = inAnnex new duc
 			, checkPresentCheap = repoCheap r
 			, exportActions = exportUnsupported
 			, whereisKey = Nothing
@@ -322,8 +327,8 @@ tryGitConfigRead autoinit r
 		else []
 
 {- Checks if a given remote has the content for a key in its annex. -}
-inAnnex :: Remote -> Key -> Annex Bool
-inAnnex rmt key
+inAnnex :: Remote -> DeferredUUIDCheck -> Key -> Annex Bool
+inAnnex rmt duc key
 	| Git.repoIsHttp r = checkhttp
 	| Git.repoIsUrl r = checkremote
 	| otherwise = checklocal
@@ -336,9 +341,12 @@ inAnnex rmt key
 			, giveup "not found"
 			)
 	checkremote = Ssh.inAnnex r key
-	checklocal = guardUsable r (cantCheck r) $
-		maybe (cantCheck r) return
-			=<< onLocalFast rmt (Annex.Content.inAnnexSafe key)
+	checklocal = ifM duc
+		( guardUsable r (cantCheck r) $
+			maybe (cantCheck r) return
+				=<< onLocalFast rmt (Annex.Content.inAnnexSafe key)
+		, cantCheck r
+		)
 
 keyUrls :: Remote -> Key -> [String]
 keyUrls r key = map tourl locs'
@@ -357,10 +365,10 @@ keyUrls r key = map tourl locs'
 	remoteconfig = gitconfig r
 	cfg = remoteGitConfig remoteconfig
 
-dropKey :: Remote -> Key -> Annex Bool
-dropKey r key
-	| not $ Git.repoIsUrl (repo r) =
-		guardUsable (repo r) (return False) $
+dropKey :: Remote -> DeferredUUIDCheck -> Key -> Annex Bool
+dropKey r duc key
+	| not $ Git.repoIsUrl (repo r) = ifM duc
+		( guardUsable (repo r) (return False) $
 			commitOnCleanup r $ onLocalFast r $ do
 				ensureInitialized
 				whenM (Annex.Content.inAnnex key) $ do
@@ -369,13 +377,15 @@ dropKey r key
 						logStatus key InfoMissing
 					Annex.Content.saveState True
 				return True
+		, return False
+		)
 	| Git.repoIsHttp (repo r) = giveup "dropping from http remote not supported"
 	| otherwise = commitOnCleanup r $ Ssh.dropKey (repo r) key
 
-lockKey :: Remote -> Key -> (VerifiedCopy -> Annex r) -> Annex r
-lockKey r key callback
-	| not $ Git.repoIsUrl (repo r) =
-		guardUsable (repo r) failedlock $ do
+lockKey :: Remote -> DeferredUUIDCheck -> Key -> (VerifiedCopy -> Annex r) -> Annex r
+lockKey r duc key callback
+	| not $ Git.repoIsUrl (repo r) = ifM duc
+		( guardUsable (repo r) failedlock $ do
 			inorigrepo <- Annex.makeRunner
 			-- Lock content from perspective of remote,
 			-- and then run the callback in the original
@@ -386,6 +396,8 @@ lockKey r key callback
 						( liftIO $ inorigrepo $ callback vc
 						, failedlock
 						)
+		, failedlock
+		)
 	| Git.repoIsSsh (repo r) = do
 		showLocking r
 		Just (cmd, params) <- Ssh.git_annex_shell ConsumeStdin
@@ -544,11 +556,13 @@ copyFromRemoteCheap _ _ _ _ = return False
 #endif
 
 {- Tries to copy a key's content to a remote's annex. -}
-copyToRemote :: Remote -> Key -> AssociatedFile -> MeterUpdate -> Annex Bool
-copyToRemote r key file meterupdate
-	| not $ Git.repoIsUrl (repo r) =
-		guardUsable (repo r) (return False) $ commitOnCleanup r $
+copyToRemote :: Remote -> DeferredUUIDCheck -> Key -> AssociatedFile -> MeterUpdate -> Annex Bool
+copyToRemote r duc key file meterupdate
+	| not $ Git.repoIsUrl (repo r) = ifM duc
+		( guardUsable (repo r) (return False) $ commitOnCleanup r $
 			copylocal =<< Annex.Content.prepSendAnnex key
+		, return False
+		)
 	| Git.repoIsSsh (repo r) = commitOnCleanup r $
 		Annex.Content.sendAnnex key noop $ \object ->
 			withmeter object $ \p -> do
@@ -717,3 +731,26 @@ mkCopier remotewanthardlink rsyncparams = do
 				)
 		, return copier
 		)
+
+{- Normally the UUID is checked at startup, but annex-checkuuid config
+ - can prevent that. To avoid getting confused, a deferred
+ - check is done just before the repository is used. This returns False
+ - when the repository UUID is not as expected. -}
+type DeferredUUIDCheck = Annex Bool
+
+mkDeferredUUIDCheck :: Git.Repo -> UUID -> RemoteGitConfig -> Annex DeferredUUIDCheck
+mkDeferredUUIDCheck r u gc
+	| remoteAnnexCheckUUID gc = return (return True)
+	| otherwise = do
+		v <- liftIO newEmptyMVar
+		return $ ifM (liftIO $ isEmptyMVar v)
+			( do
+				r' <- tryGitConfigRead False r
+				u' <- getRepoUUID r'
+				let ok = u' == u
+				void $ liftIO $ tryPutMVar v ok
+				unless ok $
+					warning $ Git.repoDescribe r ++ " is not the expected repository. The remote's annex-checkuuid configuration prevented noticing the change until now."
+				return ok
+			, liftIO $ readMVar v
+			)
diff --git a/Types/GitConfig.hs b/Types/GitConfig.hs
index 9a48ad173..ad22dadb8 100644
--- a/Types/GitConfig.hs
+++ b/Types/GitConfig.hs
@@ -199,6 +199,7 @@ data RemoteGitConfig = RemoteGitConfig
 	, remoteAnnexPush :: Bool
 	, remoteAnnexReadOnly :: Bool
 	, remoteAnnexVerify :: Bool
+	, remoteAnnexCheckUUID :: Bool
 	, remoteAnnexExportTracking :: Maybe Git.Ref
 	, remoteAnnexTrustLevel :: Maybe String
 	, remoteAnnexStartCommand :: Maybe String
@@ -247,6 +248,7 @@ extractRemoteGitConfig r remotename = do
 		, remoteAnnexPull = getbool "pull" True
 		, remoteAnnexPush = getbool "push" True
 		, remoteAnnexReadOnly = getbool "readonly" False
+		, remoteAnnexCheckUUID = getbool "checkuuid" True
 		, remoteAnnexVerify = getbool "verify" True
 		, remoteAnnexExportTracking = Git.Ref
 			<$> notempty (getmaybe "export-tracking")
diff --git a/doc/bugs/Missing_automounts_block_every_command.mdwn b/doc/bugs/Missing_automounts_block_every_command.mdwn
index 12a3463e8..53af6f15a 100644
--- a/doc/bugs/Missing_automounts_block_every_command.mdwn
+++ b/doc/bugs/Missing_automounts_block_every_command.mdwn
@@ -42,3 +42,6 @@ Use any git-annex command and wait for at least `x-systemd.device-timeout`:
 ### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)
 
 I’m very happy with git-annex (thanks) and use it frequently enough to notice this behavior.
+
+> [[fixed|done]] via the `remote.<name>.annex-checkuuid` config setting
+> that can disable this behavior. --[[Joey]]
diff --git a/doc/bugs/Missing_automounts_block_every_command/comment_4_c3cfb1c27806c45dfa6ebf275c175d3e._comment b/doc/bugs/Missing_automounts_block_every_command/comment_4_c3cfb1c27806c45dfa6ebf275c175d3e._comment
new file mode 100644
index 000000000..31f97beeb
--- /dev/null
+++ b/doc/bugs/Missing_automounts_block_every_command/comment_4_c3cfb1c27806c45dfa6ebf275c175d3e._comment
@@ -0,0 +1,13 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 4"""
+ date="2018-01-10T17:37:42Z"
+ content="""
+Added remote.<name>.annex-checkuuid config, which can be set to false
+to disable the default checking of the uuid. It will still check before
+making any modification of the remote repository.
+
+There may still be situations where using this kind of automount is suboptimal
+with git-annex, as outlined in comment 3, but I think this is as far as it makes
+sense to change git-annex to deal with them.
+"""]]
diff --git a/doc/git-annex.mdwn b/doc/git-annex.mdwn
index d4502cdfa..f427d9409 100644
--- a/doc/git-annex.mdwn
+++ b/doc/git-annex.mdwn
@@ -1234,6 +1234,18 @@ Here are all the supported configuration settings.
 
   git-annex caches UUIDs of remote repositories here.
 
+- `remote.<name>.annex-checkuuid`
+
+  This only affects remotes that have their url pointing to a directory on
+  the same system. git-annex normally checks the uuid of such
+  remotes each time it's run, which lets it transparently deal with
+  different drives being mounted to the location at different times.
+
+  Setting annex-checkuuid to false will prevent it from checking the uuid 
+  at startup (although the uuid is still verified before making any
+  changes to the remote repository). This may be useful to set to prevent
+  unncessary spin-up or automounting of a drive.
+
 * `remote.<name>.annex-trustlevel`
 
   Configures a local trust level for the remote. This overrides the value